When aircraft are moved on the ground they are conventionally either towed by a tow tractor or are powered by the propulsive force of their own main engines (i.e. the same engines that are used during flight).
As aircraft engines are optimised for the flight phase of their operation it is recognised that it would be desirable to reduce the use of the main engines to propel the aircraft on the ground. More specifically, there is believed to be a direct fuel burn saving to an aircraft if the engines are not running during the taxi phase. There may also be an additional gain in efficiency from more accurately predicting the fuel consumption during taxi phase and thereby enabling the fuel carried during flight to be reduced. Reducing the use of engines during taxi is also desirable to reduce the local emissions while the aircraft is on the ground and/or to reduce noise emissions during ground operations.
While conventional towing offers some of these advantages its use as a means for ground movement, particularly for commercial aircraft, is often limited due to the structural impact upon the landing gear of the aircraft (typically the nose landing gear). For example, older aircraft may not have been designed for extended towing operation as this would impose a significant weight penalty (due to the need to increase the weight of the landing gear structure to accommodate extra loads) and, therefore, the use of towing must be limited in order to avoid a reduction in the life of the landing gear. As such the use of towing to move an aircraft is often limited to use for either short distances or when the aircraft is only lightly loaded. For example towing is commonly used at a departure gate to push an aircraft back into a taxi area (i.e. relatively short distance) or may be used when an aircraft is being serviced (i.e. relatively low aircraft weight). For longer distance or higher weight operations such as the taxi phase prior to take off (i.e. relatively high weight and relatively long distance) and the taxi phase after landing, the aircraft's engines are used to propel the aircraft.
Accordingly, it has been proposed to provide a drive system inside, or in close proximity to, the nose wheel of an aircraft in order to enable the aircraft to be moved during taxiing or other ground handling operations of an aircraft without the use of the main aircraft engines and without the need to be dependent upon an external means such as a tow truck. An example of such a system has been proposed by WheelTug Plc. Such systems may present an additional benefit over the use of conventional systems and a tow tractor since they may allow the aircraft fully autonomous operation removing the potential for delays, for example when waiting for a tow truck during push back.
The reduction of the use of the main engines for during ground operation may be particularly desirable on short-haul aircraft where a larger proportion of the aircrafts operational time is spent in taxi and other ground handling operations. In a long haul aircraft the additional fuel burn penalty of the extra weight of a drive system may make the benefits less desirable.
Most aircraft have brakes on some or all of the main landing gear wheels. Additional brakes on the nose landing gear wheels are common, but occasionally feature as optional equipment. The additional nose landing gear brakes enable shorter stopping distances, particularly after a rejected take-off (RTO).
It has previously been proposed that passenger aircraft in the 100-200 passenger range with a tricycle landing gear configuration can be driven during taxiing without main engines by motors mounted on the nose landing gear, normally within the nose landing gear wheels. However, the problem with this arrangement is that there is insufficient traction between the nose landing gear wheels and the taxiway to move an aircraft via a nose wheel drive in anything other than ideal conditions. If the centre of gravity of the aircraft is aft of its optimum, if the aircraft has to travel uphill, if there are headwinds or if the surface is slippery, then insufficient traction exists to drive the aircraft.
It is an object of the invention to provide an improved aircraft landing gear arrangement.